This invention relates to sanding devices and in particular drum sanders suitable for sanding wood, plastics or metals.
A number of drum sanders are known in the sanding art and these sanders are most commonly used for sanding the contours of oddly shaped wood items. One type of drum sanders uses rubber wafers and it requires that special sanding sleeves be used. Because of the special nature of these sleeves, they tend to be expensive and hard to replace. The external diameter of the rubber wafers can be expanded to secure the sanding sleeve by tightening a bottom nut mounted on a threaded shaft. The wafers are also mounted in series on the threaded shaft and are squeezed between a washer mounted next to the bottom nut and a wide end portion of the shaft.
Another type of sanding drum is made by Singley Speciality Company of Hendersonville, N.C. and it employs a solid one-piece drum covered by a rubber-like layer. A hole extends from one end of the drum to the other and it is spaced a short distance from one side of the drum. A slot extends between this hole and the outer surface of the drum. An ordinary sheet of sandpaper can be mounted to this type of sander by bending the ends of the sheet to fit through the lengthwise slot. An oval aluminium tube is placed in the round hole and is then turned approximately 90 degrees with a special key in order to secure the sheet of sandpaper in place. There are several problems with this type of sanding drum including the fact that it is very difficult to secure the sandpaper properly. The oval tube often rips the sandpaper as it is being inserted into the hole and the tube can easily be bent out of shape since it is made of soft aluminium. Sometimes the tube can be hard to remove from the hole. In addition, it is difficult to tighten the sandpaper snuggly around the drum with this sanding device. If thick sandpaper is required, it can be even more difficult to attach to the drum.
An early type of sanding drum (also called a buffing mandrel) is shown in U.S. Pat. No. 141,523 dated Aug. 5, 1873 and issued to N. S. Thompson. This sanding device consisted of a drum divided diametrically into two half sections. The semi-cylindrical blocks forming the drum are attached together at one side by a hinge mechanism. At the axial centre of each semi-cylindrical block is half of a shaft which is threaded where the shaft projects from the blocks. The two halves of the shaft are connected together by means of two nuts with one nut being located at each end of the drum. In order to attach a sheet of sandpaper to the drum, the two halves are separated and the two ends of the sheet of sandpaper are fastened in place by means of pins which project from the diametrical surfaces of the two halves.
A newer drum sander having some similarities to the sander taught by the Thompson patent is that shown in U.S. Pat. No. 2,652,666 to T. Longbotham dated Sept. 22, 1953. This known sander has a split drum and the two halves are connected together at one side by means of a hinge. The two halves are covered with a thick band of synthetic rubber which is vulcanized upon the cylindrical outer surfaces. When a new sheet of sandpaper has been put in place, the two halves are brought together and are fastened at the centre by means of a conical collar. Spikes are embedded in each half of the drum sander and are located on the diametrical surface opposite the hinge side. These spikes are used to fasten in place the ends of the sheet of sandpaper. Some of the problems with these known drum sanders include the cost of making these sanders and the fact that they are not suitable for a sander having a diameter of less than one inch. It is believed that it would be difficult to manufacture a sander of the type taught by Longbotham if the diameter of the sander is to be three-quarters inch because the central shaft would have to be very small and it would not have the necessary strength. Furthermore, if a fairly long drum sander is required, a conical locking collar might be necessary at each end of the drum and a single collar would not suffice.
A deficiency in known sanding drums such as those taught by Thompson and Longbotham is that there is no mechanism provided for ensuring that the sheet of sandpaper will always be properly aligned on and arranged on the drum. With the known sanders it is easy to install the sandpaper improperly on the drum, particularly if the sheet of sandpaper has not been cut exactly in the correct manner. If the sandpaper is installed so that it projects beyond one end of the drum, it will not tighten equally around the full outer surface of the drum.
Another possible problem with known drum sanders occurs when thin sandpapers are being used. With such papers, the retention ability of the pins embedded in the diametrical surfaces of the two halves may not be sufficient. In fact thin sandpapers can tear at the location where they are pierced by the pins under heavy usage. With thicker sandpapers, there is less of a problem because these papers are sandwiched between the drum halves and the clamping force exerted by the drum halves helps the pins to retain the ends of the sandpaper.
It is an object of the invention to provide a sanding device with improved means for attaching an abrasive sheet.
It is a further object to provide sheet attachment means that makes it easier to properly align the sheet on a sanding drum.
The invention is directed to a sanding drum provided with two slots each of which is formed in a half section of the drum and extends from the diametrical surface thereof. These slots assist in the proper alignment of the sanding sheet on the drum and they can also help to hold the ends of the sheet of sandpaper in place.